Heat pump



FIG. 1 is a top plan view of a heat pump showing my new design;

FIG. 2 is a right side elevational view thereof, the left side being a mirror image thereof;

FIG. 3 is a front elevational view thereof, the back elevational view being a mirror image thereof;

FIG. 4 is a bottom plan view thereof. 

The ornamental design for a heat pump, as shown. 